This is a function for MySQL 5.0. The theory behind it is generic. The name condrand is short for conditional random

DELIMITER //

CREATE FUNCTION condrand
(
a INT,
b INT
)
RETURNS INTEGER
NO SQL
BEGIN
RETURN ROUND(a + RAND() * (b-a));
END//

mysql> SELECT condrand(1,3)//
+---------------+
| condrand(1,3) |
+---------------+
| 2 |
+---------------+
1 row in set (0.00 sec)